For people in these situations, I have started tagging spots on master that I think are good places to sync, and I do bump version numbers when I do this. They aren't officially supported releases, but only in the sense that a *real* release is guaranteed not to break API or ABI compatibility with prior releases in their X.Y.* family, whereas these developer snapshots in master do not make any such promises (and thus are named "X.Y.Z-dev").
I try to do this if I really do something that breaks compatibility, or sometimes when I add something new and exciting. But I'm also very happy to do a tag and bump master's version patch number. Just send me an email, "product ABC needs to do a release next week, can you make a tag so we have unique version number?" and I'm happy to do it.
In fact, this will be even less bottlenecked on me once the TSC gets into swing and commit/merge privileges are distributed to more people.